Add new apache date format for file listings in http sources

According to Apache source code ( http://svn.apache.org/repos/asf/httpd/httpd/trunk/modules/generators/mod_autoindex.c ), the date format changed long time ago from "10-jan-2014" to "2014-01-10" .
```
apr_strftime(time_str, &rv, sizeof(time_str),
                                 "%Y-%m-%d %H:%M  ",
                                 &ts);
```
Before the date format was: "%d-%b-%Y %H:%M  "

I didn't find the specific svn revision where this changed, but Apache 2.2 already had this date format for a long time.

This patch adds a new apache date file format so it's compatible with old and new versions of mod_autoindex. 
I added CDateTime::MonthNumToMonthString in order to not touch the rest of the code.